A Kinetic Model of the Electron Atom. 319 
which in the atom makes alpha rays or helium atoms after they have 
escaped, and we have an illustration of a radioactive substance. To 
illustrate the disintegration of an atom of radium through its several 
disintegration products I made a tray in which I imbedded a ring of iron 
so as to make a magnetic field which is strong at the center and dimin- 
ishes as we go along a radius passing through a minimum and then 
through a maximum over the ring of iron. Fig. 4 is a cross-section of 
the tray and central magnet. N, S, is the central magnet. R, R, is a 
cross-section of the iron ring. A and B are binding posts by which the 
current is led in and out. The variations of the field is represented by 
lines of force. 
To use this the current is turned on the magnet and a number of 
balls are placed in the center of the tray, forming the characteristic 
figure due to the particular number as in the Mayer experiment. The 
current is then turned through the tray, causing the balls to rotate. 
When a ball at irregular intervals starts out on a tangent it will be 
caught and held by the intense field over the iron ring at R. Thus if 
the ball represents an alpha particle, the escape of beta rays and the 
gamma radiation may be explained as being due to the disturbance in 
the atom due to the rearrangement of the electrons in the atom. As 
many as eight or ten balls may escape from the system, each rearrange- 
ment of the system representing one of the products in the radioactive 
series. Fig. 5k is a photograph of this. The four white spots, one at 
the top and one at the bottom and one on either side, are balls which 
have been thrown out and caught and held stationary over the staples 
which hold the iron ring in place. At the top of the photograph is shown 
the path of a ball which is being thrown out and caught by the ring. 
Getting the conditions right is a matter of trial. Some three or four 
trays were made before one was satisfactory. The dimensions of this 
tray are as follows: Length, 10 cm.; breadth, 10 cm.; depth, 2 cm. The 
iron ring is made of a 2%-millimeter rod bent into a ring of 6 cm. 
diameter. 
No doubt many analogies will occur to the operator which have not 
been mentioned in this paper. The worst difficulty with the experiment 
is with the mercury. The mercury must be clean. Any film of dirt or 
dross on the surface of the mercury prevents the free motion of the balls. 
The magnet and tray may be connected in series, but it is more 
convenient to have two circuits which may be manipulated independently. 
Department of Physics, Indiana University. 
